The reaction for producing ethylene oxide (EO) by direct oxidation of ethylene is a highly exothermic reaction. The heat generated in this reaction must be removed as efficiently as possible to prevent a run-away reaction that wastes expensive raw material and produces undesirable by-products. The industry standard is to use small diameter tubes of about 3/4 to 2 inches that are on the average 20 to 42 feet in length and upwards of 5000 tubes per ethylene oxide reactor. Each of the tubes is welded to a tube sheet at each end and the entire tube bundle is jacketed and filled with a heat transfer medium, such as a narrow boiling range kerosene or, in high-pressure jacketed vessels, superheated water. Due to the exothermic heat generated by the reaction, the space velocity is maintained at a high rate. It is imperative that the gas flow through the reactor be uniform across the entire catalyst bed. This reaction is highly temperature dependent and must be controlled within a narrow range to provide optimum selectivity.
As part of the ethylene oxide production, a catalyst is utilized. The catalyst is an alumina solid, much in the shape of a thick walled cylinder, about 3/8 inch in length and about 5/16 inch in overall diameter. There is also a 2/16 inch internal bore through the cylinder. The catalyst may also be produced as pellet material (3/8 in..times.3/8 in.). For ethylene oxide reactors with smaller diameter tubes, the catalyst will be made in proportionately smaller particles. The EO catalyst is impregnated with metallic silver, and may also contain various fillers.
As the activity of the catalyst begins to decline, the temperature of the reaction is raised to continue to produce ethylene oxide at an economical rate. However, there are limitations to the catalyst life and within a number of years the selectivity declines to where the catalyst must be replaced. The reactor is then opened and the old catalyst is unloaded and the reactor is reloaded with new catalyst.
Upon removal of the old catalyst the metal tubes must be loaded as quickly and efficiently as possible, since the metal tubes must not rust from ambient moisture and air. Iron oxide is an initiator of impurity formation in the direct oxidation of ethylene to ethylene oxide.
Various schemes have been proposed in an attempt to load multiple tubes simultaneously; however, experience over the past thirty years has shown that a single tube loader is often the preferred method. The ethylene oxide catalyst is a silver impregnated alumina particle, much in the shape of a thick-walled cylinder. Previous methods for loading the catalyst have utilized a gravity feed funnel with a single electrical motor driving a mechanical stirrer that kept the catalyst flowing at a certain rate. The disadvantage of this funnel arrangement was the breakage of the catalyst.
There presently exists a need in the art for an efficient and expeditious method of loading EO catalyst into reactor tubes which prevents damage to the catalyst material and at the same time affords maximum control over the catalyst drop rate and consequently, control over the packing density of the catalyst within the reactor tubes.